The objective of this work is a biophysical characterization of arterial wall with respect to its permeability to solutes of different sizes and ionic charge. Low density lipoprotein, the accumulation of which the arterial wall, leads to atherosclerosis will be included in the solutes to be tested. The permeability, parameters to be determined are: hydraulic conductivity (Lp), solute permeability coefficients (w) and solute reflection coefficients (sigma). An analysis of the results will indicate the overall porosity of arterial wall and its selectivity towards low density lipoprotein. Emphasis will be placed on the permeabilty properties of the endothelium - intimal layer. Endothelial integrity, which may be difficult to maintain in vitro, particularly using previous techniques, will be monitored by the silver-nitrate strain microscopy technique and attempts will be made according to the current state of art to maintain endothelial integrity. One of the objectives of the proposed work will be to characterize the effects of vasoactive agents on the porosity and selectivity of the aortic wall to molecules of different sizes. Agents like angiotensin II, nor-epinephrine, theophylline and Ca ion-antagonists will be used at concentrations which are optimal in their effect on aortic smooth muscle cell relaxation and contraction. We now have standardized a method for the determination of Lp and sigma of aortic wall in cylindrical geometry. Using this prodecure we have found that angiotensin II at a concentration 5x10 to the minus 7th power - a level exerting maximal contractile effect, increased both Lp and sigma compared to control. The method of "extraction in a single pass" for the determination of omega for arterial wall in situ has also been standardized.